Road construction



Patented Nov. 10, 1925.

RAYMOND W. COBURN, OF WESTON, MASSAGHUSEITS.

BOLD GOHSTRUCTION.

11o Drawing.

To all whom it may concern:

Be it known that I, RAYMOND W. CoBURN, a citizen of the United States, residing at Weston, in' the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Road Construction, of which the following is a specification.

This invention relates to road construction and has for its object simplicity of construction, and minimum building and maintenance costs.

The invention finds its principal use in the construction of bituminous macadam roads, though it may also be used for the base course or portion of other roads and pavements, for-example a pavement having a hot mix sheet asphalt. or bituminous concrete wearing surface. Though it is desirable that a macadam road in service have a rigid base, it has not proved practicable to lay a macadam surface upon a hardened concrete base because the necessary rolling of the bare rock of the macadam surface'upon the unyielding concrete of the base course would crush the macadam surface rock. Obviously a macadam surface could not be laid and rolled upon a freshly poured green concrete base. In the road construction of this invention provision is made to set up Or harden the base course after the wearing surface hasbeen com leted, the base portion being temporarily exible to allow the rolling of the surface, but later acquiring rigidity and a permanent bond of. the surface to the base portion by reasonof the setting of a mortar ap lied in a dry state.

The construction of the present pavement in its preferred form is begun by preparing the sub-grade upon which is placed a layer of clean, broken stone, say 4 or 5 inches in de th. This should referably be principally No. 1 stone rom 2 to 1%"). After this stone has been rolled to a comact condition there is then applied to it a dry mortar of cement and sand (for example a 1:2 mix). A suitable quantity is pounds of dry mortar to 500 pounds of rock or broken stone. This should be well mixed and then spread over the surface of the rock into which it is brushed and rolled until the rock will not carry any more mortar. The surplus is then broomed ofl and the top is left in a. mosaic condition. For the purpose Application filed July 29,

1925. Serial No. 48,888.

of spreading the dry mortar, a spreading machine with a mechanical agitation baflle board gives more uniform results than when the mortar is spread by hand, though the latter means, if carefully done, is entirely satisfactory. After the mortar has been spread, brushed in and rolled, additional clean rock or broken No. 1 stone (preferably without any smaller sizes) is then spread and rolled. The rolling can be thoroughly done Without danger of crushing the surface rock as the entire structure is flexible at this time, being simply keyed by the stone and the dry mortar. Upon the surface of the road is now sprayed the heated bituminous material (natural asphalt, oil asphalt, or tar) from a pressure machine in the usual manner of penetrating bituminous macadam, after which-a finishing layer of pea stone or chips is spread and rolled, and a seal coat of bituminous material applied, and this in turn covered with stone chips. In some cases in order to insure a thorough and uniform hydration of the base course the application of the seal coat may be delayed a day or two and the road meanwhile being periodically sprinkled, without interruption of traflic on the road. If desired, some sprinkling may be done before the bitumen is applied. The pavement is now com leted except for the curing or setting of t e base course. This may be done in various ways depending somewhat on the climate and sub-soil. The curing can ordinarily be accomplished in any manner which keeps the shoulders of the road moist or wet, for example by drenching the shoulders at regular intervals with a Watering cart, pipe lines with sprays radiating therefrom along the sides of the road, or by means of low dikes or pending water along the sides of the road.

It has been found that the road as thus described will set up so that the base portion, though not containing nearly so much cement as is ordinarily used in a Portland cement concrete base, approaches the strength of a standard concrete base and with a far better bond of the surface to the base portion because, after the surface rgck is-placed, the mortar is slowly cured and kept moist by the ercolation and ca illary action, as well as eing kept from rying out by the water-impervious wearing surface. The strength of a road is often brought up to that of one having 9. Portland cement concrete base at a considerable saving of labor and without loss of use in connection with the usual covering of a base with loam for a long curing period. Thus a road of this construction can be used immediately after it is laid, without first allowing the same to set and without keeping traific off of it while it sets. Because the surface rock is rolled down into the base portion before the mortor has set it keys or bonds with the base portion and is held by the mortar. The addition of the small amount of cement mortar in a dry state has proved to be a real economy in time and labor and when the mortar is moistened in this manner there is no formation of an objectionable laitance or scum impairing the bond which is often the case with a poured concrete base. The dry mortar is easily worked in and stays put, being there comparted and held in place by the rolling and keying of the stone, and since it is then set up slowly as the moisture reaches it the danger of weak spots due to the washing away of cement particles is eliminated. In this respect it has a distinct advantage over one practice of using a thin liquid cement grout.

The above procedure of applying stone may be modified by placing the broken stone in one layer, applying the dry mortar to within a specified distance from the top, sprinkling to clean the surface rock (and incidentally to start hydration), and then rolling and applying the bituminous surfacing. Ineither case the net result is substantially the same.

I claim 1. The method of road construction which consists in reparing a suitable sub-grade, depositing t ereon crushed stone and dry mortar, and placin bituminous material on the same before. said mortar has set.

2. The method of road construction which consists in preparing a suitable sub-grade, depositing thereon crushed stone and dry mortar and penetrating the. surface-of said stone with bituminous material before the said mortar has set.

3. The method of road construction which consists in preparing a suitable sub-grade, depositin thereon crushed rock and dry mortar, epositing additional rock, and applying bitumen thereto.

4. The method of road construction which consists in preparing a suitable sub-grade, depositing roc an dry mortar thereon, and applying a hot-mix bituminous surface mixture.

5. The method of road construction which consists in pre arin a suitable sub-grade, depositing roc an dr mortar on said sub-grade, depositing an rolling additional rock thereon, and penetrating the surface rock with bitumen.

6. The steps in constructing a bituminous surfaced road which consist in depositing and working dry mortar into the base portion of the road, and completing the surface of said road before the mortar has set.

RAYMOND W. COBURN. 

